In the molding of plastic parts by injection molding, mold parts are brought together to define a mold cavity, polymeric material is injected into the mold cavity and, after allowing time for the polymer to solidify, the mold parts are drawn apart and the molded part removed.
The moveable elements or plattens of the molding machine are arranged to move in a horizontal direction and slide on stationary bars to transport the moveable mold parts into and out of mating relationship with a stationary mold part.
Such molds may be single face, with a single moveable mold part and a stationary mold part or may be a stack mold where two or more moveable mold parts move towards and away from a stationary mold part.
In the latter molding machines, a rack-and-pinion structure often is used to achieve synthronized self-positioning of the moveable mold parts. In such devices, rack elements are attached to the stationary mold part and the outer moveable mold part, while a pinion is mounted to the inner moveable mold part. Depending on the size of the stack mold, one or more such rack-and-pinion structures may be provided on each side of the stack mold.
In general, the rack-and-pinion structure is custom-made for a specific stack mold and it is necessary to precisely position the device on the mold parts of the stack mold to ensure correct mold operation in the molding machine. When access to the mold parts is required for removal from the molding machine and replacement by another stack mold, the rack-and-pinion structure often needs to be first removed and then subsequently reassembled, a time consuming operation.